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Structure of the Sun
in the He-shell]] Structure of sun Core of Sun )]] The core of the Sun is considered to extend from the center to about 0.2 solar radii. It has a density of up to 150,000 kg/m³ (150 times the density of water on Earth) and a temperature of close to 13,600,000 kelvin (by contrast, the surface of the Sun is around 5,800 kelvin). Recent analysis of SOHO mission data favors a faster rotation rate in the core than in the rest of the radiative zone.Garcia R. A. et al. "Tracking Solar Gravity Modes: The Dynamics of the Solar Core", Science, American Association for the Advancement of Science, 316, 5831, 1591 - 1593 (2007) Through most of the Sun's life, energy is produced by nuclear fusion through a series of steps called the p–p (proton–proton) chain; this process converts hydrogen into helium. The core is the only location in the Sun that produces an appreciable amount of heat via fusion: the rest of the star is heated by energy that is transferred outward from the core. All of the energy produced by fusion in the core must travel through many successive layers to the solar photosphere before it escapes into space as sunlight or kinetic energy of particles. About 3.4 protons (hydrogen nuclei) are converted into helium nuclei every second (out of ~8.9 total amount of free protons in the Sun), releasing energy at the matter–energy conversion rate of 4.26 million tonnes per second, 383 yottawatts (3.83 W) or 9.15 megatons of TNT per second. This actually corresponds to a surprisingly low rate of energy production in the Sun's core—about 0.3 W/m³ (watts per cubic meter). This is less power than generated by a candle. Power density is about 6 µW/kg of matter. For comparison, the human body produces heat at approximately the rate 1.2 W/kg, roughly a million times greater per unit mass. The use of plasma with similar parameters for energy production on Earth would be completely impractical—even a modest 1 GW fusion power plant would require about 170 billion tonnes of plasma occupying almost one cubic mile. Hence, terrestrial fusion reactors utilize far higher plasma temperatures than those in Sun's interior. The rate of nuclear fusion depends strongly on density and temperature, so the fusion rate in the core is in a self-correcting equilibrium: a slightly higher rate of fusion would cause the core to heat up more and expand slightly against the weight of the outer layers, reducing the fusion rate and correcting the perturbation; and a slightly lower rate would cause the core to cool and shrink slightly, increasing the fusion rate and again reverting it to its present level. The high-energy photons (gamma rays) released in fusion reactions are absorbed in only few millimetres of solar plasma and then re-emitted again in random direction (and at slightly lower energy)—so it takes a long time for radiation to reach the Sun's surface. Estimates of the "photon travel time" range between 10,000 and 170,000 years. After a final trip through the convective outer layer to the transparent "surface" of the photosphere, the photons escape as visible light. Each gamma ray in the Sun's core is converted into several million visible light photons before escaping into space. Neutrinos are also released by the fusion reactions in the core, but unlike photons they rarely interact with matter, so almost all are able to escape the Sun immediately. For many years measurements of the number of neutrinos produced in the Sun were lower than theories predicted by a factor of 3. This discrepancy was recently resolved through the discovery of the effects of neutrino oscillation: the Sun in fact emits the number of neutrinos predicted by the theory, but neutrino detectors were missing 2/3 of them because the neutrinos had changed flavor. Radiative zone From about 0.25 to about 0.7 solar radii, solar material is hot and dense enough that thermal radiation is sufficient to transfer the intense heat of the core outward. In this zone there is no thermal convection; while the material grows cooler as altitude increases (from 7,000,000 °C to about 2,000,000 °C) this temperature gradient is less than the value of adiabatic lapse rate and hence cannot drive convection. Heat is transferred by radiation—ions of hydrogen and helium emit photons, which travel only a brief distance before being reabsorbed by other ions. The density drops a hundredfold (from 20 g/cm³ to only 0.2 g/cm³) from the bottom to the top of the radiative zone. Between the radiative zone and the convection zone is a transition layer called the tachocline. This is a region where the sharp regime change between the uniform rotation of the radiative zone and the differential rotation of the convection zone results in a large shear—a condition where successive horizontal layers slide past one another. The fluid motions found in the convection zone above, slowly disappear from the top of this layer to its bottom, matching the calm characteristics of the radiative zone on the bottom. Presently, it is hypothesized (see Solar dynamo), that a magnetic dynamo within this layer generates the Sun's magnetic field. Convective zone In the Sun's outer layer, from its surface down to approximately 200,000 km (or 70% of the solar radius), the solar plasma is not dense enough or hot enough to transfer the heat energy of the interior outward via radiation (in other words it is opaque enough). As a result, thermal convection occurs as thermal columns carry hot material to the surface (photosphere) of the Sun. Once the material cools off at the surface, it plunges back downward to the base of the convection zone, to receive more heat from the top of the radiative zone. At the visible surface of the Sun, the temperature has dropped to 5,700° K and the density to only 0.2 g/m³ (about 1/10,000th the density of air at sea level). The thermal columns in the convection zone form an imprint on the surface of the Sun, in the form of the solar granulation and supergranulation. The turbulent convection of this outer part of the solar interior gives rise to a "small-scale" dynamo that produces magnetic north and south poles all over the surface of the Sun. The Sun's thermal columns are Bénard cells and therefore tend to be hexagonal prisms. Photosphere , or black body temperature, of the Sun (5777 K) is the temperature a black body of the same size must have to yield the same total emissive power.]] The visible surface of the Sun, the photosphere, is the layer below which the Sun becomes opaque to visible light. Above the photosphere visible sunlight is free to propagate into space, and its energy escapes the Sun entirely. The change in opacity is due to the decreasing amount of H− ions, which absorb visible light easily. Conversely, the visible light we see is produced as electrons react with hydrogen atoms to produce H− ions. }} The photosphere is actually tens to hundreds of kilometers thick, being slightly less opaque than air on Earth. Because the upper part of the photosphere is cooler than the lower part, an image of the Sun appears brighter in the center than on the edge or limb of the solar disk, in a phenomenon known as limb darkening. Sunlight has approximately a black-body spectrum that indicates its temperature is about 6,000 K, interspersed with atomic absorption lines from the tenuous layers above the photosphere. The photosphere has a particle density of ~1023 m−3 (this is about 1% of the particle density of Earth's atmosphere at sea level). During early studies of the optical spectrum of the photosphere, some absorption lines were found that did not correspond to any chemical elements then known on Earth. In 1868, Norman Lockyer hypothesized that these absorption lines were because of a new element which he dubbed "helium", after the Greek Sun god Helios. It was not until 25 years later that helium was isolated on Earth. Inverse biquadrate force and Photogravitational mass In the inverse biquadrate scheme, Gravitational mass of the Sun is given as follows, M_s = (d_{ms})^5 (\omega_{ms})^2 / G'' where G" =9.431 10^8 m^5/kg/sec^2 Gravitational density of moon is 228.4 ton/m^3 Gravitational density of sun is 6.78*228.4 ton/m^3 Above values are photo-gravitational mass which is given as follows, m_{pg} = m_i T_s /T_0 And the inertial density of the sun is determined with structure of the sun, Example is given for Structure of the Earth Simple calculation gives a temperature of radiative zone about 23067K with gravitational mass density of 1548 ton/m^3 See also *Structure of the Earth *Photogravity * Photogravitational mass *Inertial confinement fusion *Density of the moon *Density of Sun Notes and references Category:Gravity wikia